THE ROLE OF HERBIVORES IN SHAPING CORAL REEF MACROALGAL COMMUNITIES: DIFFERING EFFECTS OF HERBIVOROUS FISH AND THE LONG- SPINED SEA URCHIN Diadema antillarum By LINDSAY J. SPIERS A DISSERTATION PRESENTED TO THE GRADUATE SCHOOL OF THE UNIVERSITY OF FLORIDA IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY UNIVERSITY OF FLORIDA 2020 © 2020 Lindsay J. Spiers To Mom and Dad ACKNOWLEDGMENTS I would like to thank Dr. Tom Frazer for all his assistance in helping me focus my many disparate ideas into a comprehensive project that I am proud of. Without all the support and advice, I would still be conducting the numerous experiments I kept designing. Thank you for giving me the freedom and encouragement I needed to grow as a scientist. I would also like to extend gratitude to the rest of my committee; Dr. Chuck Jacoby, Dr. Don Behringer, Dr. Michal Kowalewski, and Dr. Ed Phlips for all their assistance and encouragement as I took my research data and translated it into the comprehensive work I present here. I appreciate all your help with experimental design, statistical analysis, and graphing. I also must thank the members of my lab group, especially Dr. Anya Brown and Dr. Jana Hilsenroth, for all their assistance and support and their willingness to act as a sounding board for new ideas. In addition, I must thank them for all the dinners and lunches we enjoyed together that helped me remain sane as I was trying to finish graduate school. In addition, I am eternally grateful for the numerous people who assisted me with all my field work. From the scientists and interns at Carrie Bow Cay to everyone at CCMI, especially Joe Kuehl, I could have not done any of this without you. Finally, I must thank my parents for fostering my love of science and the ocean as well as continuing to support me through all my highs and lows of graduate school. 4 TABLE OF CONTENTS page ACKNOWLEDGMENTS ...............................................................................................................4 LIST OF TABLES ...........................................................................................................................7 LIST OF FIGURES .........................................................................................................................8 ABSTRACT ...................................................................................................................................11 CHAPTER 1 REVIEW OF THE CURRENT STATE OF CARIBBEAN CORAL REEFS .......................13 Coral Reef Stressors ...............................................................................................................14 Regional Stressors: Atlantic and Caribbean ...........................................................................21 Algae on Coral Reefs ..............................................................................................................24 Herbivores on Caribbean Coral Reefs ....................................................................................27 2 ANALYSIS OF THE BENTHIC COMMUNITY STRUCTURE ON SHALLOW PATCH REEFS NEAR CARRIE BOW CAY, BELIZE .......................................................37 Introduction .............................................................................................................................37 Methods ..................................................................................................................................40 Results.....................................................................................................................................43 Discussion ...............................................................................................................................46 3 THE EFFECT OF HERBIVOROUS FISHES AND Diadema antillarum ON THE ESTABLISHMENT OF A MACROALGAL COMMUNITY ON A SHALLOW BELIZEAN CORAL REEF ...................................................................................................59 Introduction .............................................................................................................................59 Methods ..................................................................................................................................62 Caging Experiment ..........................................................................................................63 In Cage Feeding Experiment ...........................................................................................66 Herbivore Feeding Assays ...............................................................................................67 Results.....................................................................................................................................70 In Cage Feeding Experiment ...........................................................................................74 Feeding Assays ................................................................................................................75 Discussion ...............................................................................................................................76 4 HOW HERBIVORES RESHAPE A MACROALGAL COMMUNITY ON A LITTLE CAYMAN CORAL REEF: THE ROLE OF HERBIVORE TYPE AND DENSITY ...........96 Introduction .............................................................................................................................96 Methods ................................................................................................................................100 5 Results...................................................................................................................................105 Discussion .............................................................................................................................113 5 ANALYSIS OF FEEDING CHOICE OF HERBIVOROUS FISH AND Diadema antillarum IN LITTLE CAYMAN .......................................................................................131 Introduction ...........................................................................................................................131 Methods ................................................................................................................................135 Fish Feeding Assays ......................................................................................................136 Diadema antillarum Feeding Assay ..............................................................................138 No-choice feeding assays .......................................................................................139 Choice feeding assays ............................................................................................140 Results...................................................................................................................................141 Fish Feeding Assays ......................................................................................................141 Diadema antillarum Feeding Assay-No-choice ............................................................144 Diadema antillarum Feeding Assay-Choice .................................................................145 Discussion .............................................................................................................................146 6 CONCLUSION: FINAL THOUGHTS ON THE ROLE OF HERBIVORES ON CARIBBEAN CORAL REEFS ............................................................................................165 LIST OF REFERENCES .............................................................................................................170 BIOGRAPHICAL SKETCH .......................................................................................................183 6 LIST OF TABLES Table page 2-1 Coordinates for patch reefs that were surveyed. ................................................................50 2-2 Density of Diadema antillarum found on each patch reef. ................................................50 2-3 Depth and percent cover of three major categories of benthic organisms ± standard error (SE) on each surveyed patch reef. .............................................................................51 3-1 Algal assemblage by treatment and month sorted by percent cover. Palatability: C- chemically rich, S- structurally defended, P- palatable, U-unknown. ...............................81 3-2 Average density of fish species per m2 ± standard error (SE) on the experimental reef. * herbivorous species. ................................................................................................85 3-3 Average density of fish species per m2 ± standard error (SE) on Golden Reef where feeding assays were conducted. * represent herbivorous species. .....................................85 4-1 Mean numbers of fish ± standard errors (SE) for each species found along transects. *indicates roaming herbivores .........................................................................................118 4-2 Percent cover of macroalgae by genera for each month. Superscripts represent defenses: 1. Cyanobacteria, 2. Chemically rich, 3. Chemically rich and structurally defended, 4. Structurally defended, 5. Unknown.............................................................120 5-1 List of macrophytes used in feeding assays along with their known defenses and known responses of herbivores to congeners...................................................................151